In the prior art, reverse flow regeneration has required the resin bed to be held in position either by sending a flow of air or water against the flow of regenerating liquid, or else mechanically between two perforated plates.
In the mechanical case, it has been conventional to use a kind of inflatable balloon inside the apparatus containing the resin. Another known method consists in using polyethylene balls disposed between an upper perforated plate and the resin, in order to prevent the resin expanding. A third method consists in filling the space between the perforated plates with resin so that it occupies about 95% of the available space and, either in regenerating downwardly through the apparatus and passing the water to be treated flows upwardly therethrough at sufficient speed to press the resin bed against the upper plate, or else or regenerate upwardly at sufficient speed to press the resin bed against the upper plate and to pass the water to be treated downwardly during treatment.
In both variants of this method, all or part of the resin must be removed from the apparatus so as to periodically uncompact the resin in some outside device. The resin then subsequently needs to be returned to the apparatus.
Preferred implementations of the present invention avoid these drawbacks by allowing the resin to be removed and uncompacted in a single operation and by providing an expansion volume directly over the normal resin container.